This invention relates to the transmission of additional data in the active picture period of video transmissions for example such as broadcast television transmission.
Digitally assisted television (DATV) has been proposed which uses additional data transmitted with a video signal to enhance the display at the receiver and thereby produce, for example, a high definition television (HDTV) picture or some other enhanced display.
It is proposed that HDTV receivers will typically operate with a larger aspect ratio, namely the ratio of picture width to picture height, than that used with conventional receivers operating, for example, on 625 lines. Since conventional receivers are not compatible with a full bandwidth HDTV signal a method of transmitting signals which can be received on both types of receiver is needed.
A system for use with both HDTV receivers and conventional receivers is described in U.S. Pat. No. 4,613,903. This uses a high resolution TV camera to provide two transmission signals. The first of these is compatible with a conventional receiver. This signal includes the sum average of two of the HDTV fields in a first field and the remaining HDTV field in a second field. The second signal contains the remaining HDTV information. An HDTV receiver uses both transmitted signals to reconstruct an HDTV signal.
U.S. Pat. No. 4,672,425 proposes transmitting data in the active picture period of a conventional transmission and using this data to produce an extended aspect ratio picture on a non-conventional receiver. However, since the data is in the active picture period it is visible on the conventional receiver.